An installation having a large-size complicated structure, such as a hydraulic turbine runner of a hydraulic power generator, is difficult to manufacture from one article of cast metal. Hence, the installation is formed from a plurality of parts, and these parts are joined to each other by welding. In the hydraulic turbine runner, a welded portion surface is used as a flow passage, and hence a vortex flow occurs on an unshaped welded surface after the joint, resulting in an increase in loss.
In order to make a welded surface smooth, the welded surface is shaped by manual grinding. Unfortunately, this grinding work is performed in a bad environment in which a worker is exposed to dust and needs to use a vibratory tool. Further, a complicated installation has a narrow portion, and hence a large amount of labor (for example, the worker needs to hold a posture with low workability) is imposed on the worker.
In view of these situations, a plasma gouging apparatus has been proposed as a shaping method that replaces such grinding of a welded portion (see Patent Document 1). The plasma gouging apparatus uses a gouging speed and voltage as parameters to be controlled.
An automatic gouging apparatus has been also proposed as a method that replaces such grinding of a large-size complicated installation (see Patent Document 2). The automatic gouging apparatus calculates a removing amount of excess thickness by means of: an apparatus that measures an exemplary shape using an excess thickness detecting stylus and stores the exemplary shape as a reference shape; and a calculating apparatus that compares a shape of an object to be processed with the reference shape and calculates the excess thickness.
Further, the automatic gouging apparatus performs shaping while controlling the removing amount of excess thickness using an arc air gouging torch mounted on a multiaxis slider. In this manner, the automatic gouging apparatus automatically processes the object to be processed into a desired shape.